Stopping the Gulf of Mexico oil leak

BP has tried a number of methods to shut down the leak from the damaged oil well - often innovating as subsequent attempts have failed.

Although some of the methods have been tried and tested at incidents elsewhere in the world, they have not been carried out at such great depth as the Deepwater Horizon leak - 5,000 feet (1.5km) below the surface.

2 JUNE: LOWER MARINE RISER PACKAGE

After the failure of the top kill procedure, BP attempts to cut the top off the upper section of the blowout preventer (BOP) and place a cap on it, sealing the leak and taking oil to a ship on the surface.

After a brief setback with some of the cutting equipment, the cap is installed and BP announces on 4 June that it is collecting oil at a rate of 1,000 barrels a day.

Attempt to cap oil leak

The latest stage in BP's efforts to contain leaking oil has involved lowering a cap onto the failed blowout preventer (BOP) valve system on the seabed. The cap sits on the BOP's lower marine riser package (LMRP) section.
First, the damaged riser - the pipe which takes oil from the well - was cut where it nears the seabed using a remotely-operated shear. This was completed at 1930 CDT on 1 June (0030 GMT 2 June).
The next stage was for a diamond wire cutter to saw through the riser close to the LMRP. The blade got stuck and had to be removed but BP eventually cut through the pipe using giant shears manipulated by undersea robots (ROV).
After removing the pipe, the cap was lowered onto the LMRP enabling the leaking oil and gas to be funnelled to a drill ship on the surface. Latest estimates suggest more than half of the leaking oil is now being captured.
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26 MAY - 29 MAY: TOP KILL OF BLOWOUT PREVENTER - FAILED

Turning their focus to the blowout preventer or BOP that sits over the well head, BP try to stem the flow of oil and gas and ultimately kill the well by injecting heavy drilling fluids.

The procedure includes injecting a "junkshot" of golf balls, rope and rubber into the BOP in a bid to block the flow.

Despite pumping more than 30,000 barrels of heavy mud itno the BOP and a range of junkshot, the operation fails to overcome the flow from the well.

image showing BP's oil flow system, with inside the blowout preventer.
16 MAY: RISER INSERTION TUBE - SUCCESS
Insertion tube to siphone oil from leaking pipe

BP had some success with a "riser insertion tube" - a pipe with rubber diaphragm inserted into the leaking part of the riser pipe that is the source of the main oil flow from the well.

The insertion tuibe is connected to its own riser pipe that takes the oil and gas to the Transocean Discoverer Enterprise drillship, 5,000ft (1,524m) above on the surface.

Methanol is injected into the tube to stop the formation of hydrates - crystals that could block the flow of oil and gas.

The tube tool has been able to collect about 3,000 barrels a day of oil and some 14 million standard cubic feet a day of gas.

The oil is being stored and gas is being flared on the drillship Discoverer Enterprise - which has the capacity to store 139,000 barrels of oil.

8 - 18 MAY: CONTAINER DOME AND TOP HAT- FAILED

Plans to place a large containment dome over the main leak and siphon oil to a ship on the surface is aborted as hydrates or ice crystals build up, blocking the pipes.

A smaller "top hat" dome is lowered to perform a similar task, but engineers decide to use insertion tube instead.

Underwater efforts to cap oil leak

Initially, BP tried to lower a 125-tonne, 18-metre (59 feet) high container dome over the main leak on the sea floor. However, this failed when gas leaking from the pipe mixed with water to form hydrates, ice-like crystals, that blocked up the steel canopy.
Instead, engineers have lowered a smaller device onto the site. Dubbed the Top hat, it will sit over the tear in the pipe and partially stop the leak. To prevent the build up of hydrates, methanol is pumped into the top hat to disperse the water and gas.
The top hat is 1.5m (5 feet) high and 1.2m in diameter. Two special side lines are used to pump methanol into the top hat to displace water and gas leaking from the broken oil pipe. This should prevent the build-up of hydrates. Once in place, oil can be pumped up to the surface.
BP plan to lower the original subsea containment dome over the top hat to provide a better seal over the leaking site and pump oil up to the surface. This time, it will be attached to a pipe that can pump warm water into the dome to prevent the build-up of hydrates.
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2 MAY: DRILLING RELIEF WELLS - ONGOING

BP is drilling two relief wells in an additional effort to relieve the flow of oil. Work on the first relief well started on 2 May, with the second starting on 16 May. Both wells are expected to take around three months to complete from the start of drilling.

Graphic showing relief wells

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